 /*******************************************************************************
  * Copyright (c) 2006, 2007 IBM Corporation and others.
  * All rights reserved. This program and the accompanying materials
  * are made available under the terms of the Eclipse Public License v1.0
  * which accompanies this distribution, and is available at
  * http://www.eclipse.org/legal/epl-v10.html
  *
  * Contributors:
  * IBM Corporation - initial API and implementation
  *******************************************************************************/

 package org.eclipse.core.internal.databinding.observable;

 import java.util.Collection ;
 import java.util.Collections ;
 import java.util.Iterator ;
 import java.util.Set ;

 import org.eclipse.core.databinding.observable.IChangeListener;
 import org.eclipse.core.databinding.observable.IStaleListener;
 import org.eclipse.core.databinding.observable.Realm;
 import org.eclipse.core.databinding.observable.set.IObservableSet;
 import org.eclipse.core.databinding.observable.set.ISetChangeListener;

 /**
  * Singleton empty set
  */
 public class EmptyObservableSet implements IObservableSet {

     private static final Set emptySet = Collections.EMPTY_SET;

     private Realm realm;

     /**
      * Creates a singleton empty set. This set may be disposed multiple times
      * without any side-effects.
      *
      * @param realm
      */
     public EmptyObservableSet(Realm realm) {
         this.realm = realm;
     }

     public void addSetChangeListener(ISetChangeListener listener) {
     }

     public void removeSetChangeListener(ISetChangeListener listener) {
     }

     public Object getElementType() {
         return null;
     }

     public int size() {
         return 0;
     }

     public boolean isEmpty() {
         return true;
     }

     public boolean contains(Object o) {
         return false;
     }

     public Iterator iterator() {
         return emptySet.iterator();
     }

     public Object [] toArray() {
         return emptySet.toArray();
     }

     public Object [] toArray(Object [] a) {
         return emptySet.toArray(a);
     }

     public boolean add(Object o) {
         throw new UnsupportedOperationException ();
     }

     public boolean remove(Object o) {
         throw new UnsupportedOperationException ();
     }

     public boolean containsAll(Collection c) {
         return c.isEmpty();
     }

     public boolean addAll(Collection c) {
         throw new UnsupportedOperationException ();
     }

     public boolean retainAll(Collection c) {
         throw new UnsupportedOperationException ();
     }

     public boolean removeAll(Collection c) {
         throw new UnsupportedOperationException ();
     }

     public void clear() {
         throw new UnsupportedOperationException ();
     }

     public void addChangeListener(IChangeListener listener) {
     }

     public void removeChangeListener(IChangeListener listener) {
     }

     public void addStaleListener(IStaleListener listener) {
     }

     public void removeStaleListener(IStaleListener listener) {
     }

     public boolean isStale() {
         return false;
     }

     public void dispose() {
     }

     public Realm getRealm() {
         return realm;
     }

 }

